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The effects of liquid phase rheology on the local hydrodynamics of bubble column reactors operating with non-Newtonian liquids are investigated. Local bubble properties, including bubble frequency, bubble chord length, and bubble rise velocity, are measured by placing two in-house made optical fiber probes at various locations within a bubble column reactor operating with different non-Newtonian liquids. It was found that the presence of elasticity can noticeably increase the bubble frequency but decreases the bubble chord length and its rise velocity. The radial profiles of bubble frequency, bubble chord length, and bubble rise velocity are shown to be relatively flat at low superficial gas velocity while they become parabolic at high superficial gas velocity. Moreover, the bubble size and gas holdup are correlated with respect to dimensionless groups by considering the ratio between dynamic moduli of viscoelastic liquids. The novel proposed correlations are capable of predicting the experimental data of bubble size and gas holdup within a mean absolute percentage error of 9.3% and 10%, respectively. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1382–1396, 2016

In this review we critically assess numerical simulations of the interstellar medium (ISM), and argue that 3D high resolution calculations are the most promising method to determine the structure of the interstellar gas and follow its evolution well into the nonlinear regime. Based on a Riemann solver adaptive mesh refinement code, we present a model, which fulfills the basic requirements of running it sufficiently long in order to erase memory effects of the initial conditions, set up a disk-halo fountain flow cycle, for converging solutions with increasing mesh refinement. We obtain the following results: (i) in a supernova driven ISM, high Reynolds number turbulence generates structures on all scales, (ii) the volume filling factor of the hot gas is substantially reduced due to the fountain flow, (iii) gas clouds are transient shock compressed layers, (iv) more than half of the gas mass resides in thermally unstable regimes, (v) O VI is distributed in patchy mixing layers, with the derived column densities being in agreement with FUSE and Copernicus observations, (vi) the electron density distribution up to distances of 8 kpc in the disk is consistent with pulsar dispersion measure observations, provided that the electron and ionization structure are not in equilibrium, (vii) the interstellar cooling function depends both on space and time (and not only on temperature and metallicity), (viii) the Local Bubble has been produced by 14–20 supernovae about 14 Myr ago, exploding in a moving group on its path through the local ISM, (ix) the nearest supernova explosion to Earth occurred 2.2 × 106 yr ago at a distance of ∼85 pc, in agreement with measurements of the radionuclide 60Fe found in the ferromanganese crust on the ocean floor (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Charge-transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge-transfer with respect to the dynamics and the structure of neutral gas-plasma interfaces. We consider the following phenomena: (1) the heliospheric interface - region where the solar wind plasma interacts with the partly-ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so-called “Local Bubble”. In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two-component model of the cloud-plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud-plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X-ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X-ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge-transfer X-ray emission from the neutral cloud-plasma interface may be comparable to the diffuse thermal X-ray emission from the million degree gas cavity itself (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bubble size distribution was modelled by employing the population balance equation (PBE). All three bubble coalescence mechanisms (turbulence, buoyancy and laminar shear) and the main bubble breakup mechanism (breakup due to turbulent eddies) were considered in the model. Local bubble size distributions at the top and bottom of the column were obtained by solving this PBE. The results were compared with the experimental data for seven independent multiphase systems (water/air, isomax diesel/air, kerosene/air and four other liquid mixture/air) at two diverse gas velocities. The experimental adjustable constant in the coalescence efficiency function was determined by fitting the population balance to the experimental bubble size distributions. An empirical correlation was proposed for the coalescence efficiency by the dimensional analysis, which includes Reynolds and Weber numbers. © 2011 Canadian Society for Chemical Engineering

Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont ete etudies dans trois colonnes a bulles de diametres differents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde a fibre optique a embout unique employant la technique laser Doppler, des mesures locales de la retention de gaz, de la frequence des bulles, de la taille des bulles et de la vitesse ont ete effectuees simultanement a differents endroits dans les colonnes. Ces mesures ont ete effectuees pour un systeme air-eau a des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennes et les mesures instantanees ont ete analyses puis compares pour differentes colonnes. La presence d'une structure de circulation unique coherente occupant tout le diametre de la colonne dans la colonne la plus large plutot qu'une paire de cellules de circulation symetriques observees dans les colonnes plus petites est confirmee.

Computational Fluid Dynamics (CFD) can be used to investigate local reaction rates and gas-liquid mass transfer in agitated aerobic fermenters, but it is too slow for the simulation of a whole fermentation batch at present computational capabilities. This problem is addressed in the present work by developing a dynamic model with 42 subregions for a 0.64 m3 pilot xanthan fermenter. The model considers local reaction and mass transfer rates in the fermenter and the change of liquid flow fields during the fermentation. Gas-liquid mass transfer fluxes are calculated based on the simplified solution of Maxwell-Stefan diffusion by assuming the mass transfer resistance in both the gas and the liquid side of the gas-liquid interface. Gas-liquid mass transfer areas are obtained from Population Balances (PB) for bubbles. The comparison of model predictions to the laboratory stirred tank experiments with aqueous xanthan shows the need of local bubble size distributions (BSD) for the description of complex gas-liquid hydrodynamics and mass transfer. The model predicts the effect of operating conditions on the temporal and spatial variation of BSDs, mass transfer coefficients, dissolved oxygen concentrations, and xanthan reaction rates in the fermenter. It can be used to investigate fermenter operating strategies. The model is also useful for the scale-up studies. © 2006 American Institute of Chemical Engineers AIChE J, 2006

A computational fluid dynamics-population balance model (CFD-PBM) coupled model was developed that combines the advantages of CFD to calculate the entire flow field and of the PBM to calculate the local bubble size distribution. Bubble coalescence and breakup were taken into account to determine the evolution of the bubble size. Different bubble breakup and coalescence models were compared. An algorithm was proposed for computing the parameters based on the bubble size distribution, including the drag force, transverse lift force, wall lubrication force, turbulent dispersion force, and bubble-induced turbulence. With the bubble breakup and coalescence models and the interphase force formulations in this work, the CFD-PBM coupled model can give a unified description for both the homogeneous and the heterogeneous regimes. Good agreement was obtained with the experimental results for the gas holdup, liquid velocity, and bubble size distribution.

A new method is developed for the determination of bubble size distributions from experimental laser Doppler anemometry (LDA) data through simultaneous measurement of only two orthogonal velocity components and the intermittent time gaps arising out of bubbles passing through the measurement point. An experimentally verifiable assumption of axisymmetry allowed the calculation of the three-dimensional velocity distributions from the two-dimensional measurement through the elegant use of a mathematical transform called Abel's transform. In conjunction with the use of probability theory, it allows calculation of the chord length distribution. The bubble size distribution is obtained by an inversion procedure, which facilitates the transformation of chord lengths to bubble sizes. The inversion procedure is successfully tested with Monte Carlo simulations, in which bubbles of prescribed size distribution were generated for obtaining synthetic data on subtended chord lengths at any given point in the column. It is unambiguously demonstrated that assumptions that do not account for correlation between bubble size and direction of motion can yield highly erroneous size distributions from chord length data. The procedure was then used on experimental chord length distributions obtained using LDA to estimate local bubble size distributions in our bubble column. It is particularly interesting to observe that the mean bubble size estimated from the calculated bubble size distributions were consistent with an estimation based on slip velocity information in accord with the Zuber-Findlay drift flux model.

J01 Joint Evolution of the Local and Loop I Superbubbles – what can High Resolution Simulations tell us? J02 XMM-Newton Observations of the Local Bubble and the Galactic Halo J03 Soft X-ray Emission From the Local Bubble and Loop I in the Direction of the Ophiuchus Cloud J04 The Dynamic Helisophere in the Galactic Circle J05 Effects Induced by the Passage of the Sun Through Dense Molecular Clouds J06 Cosmic Ray Flux Variations at 1 AU Caused by the Solar Cycle Induced Variations of the Global Heliosphere J07 Latitudinal Solar Wind Flows Enforced by Pick up Ion Pressure Gradients J08 Lunar Soils – An Archive for the Galactic Environment of the Solar System? J09 The Relevance of the 13-months Period in the 1 AU Electron Data for Diffusive Particle Transport J10 Quiet Time MeV Electron Increases at Solar Maximum: Ulysses COSPIN/KET Observations J11 Remote Sensing of the Outer Heliosphere from 1 AU J12 Measurements of Interstellar Dust in the Heliosphere at 1 AU J13 Development of a Dust Telescope for a Dust Observatory

In der vorliegenden Arbeit wird der Einsatz der numerischen Stromungssimulation (CFD) fur das Berechnen von instationaren und dreidimensionalen Stromungsfeldern in Blasensaulen erlautert. Die lokale Blasengrosenverteilung wird mit Hilfe einer Bilanzgleichung fur das mittlere Blasenvolumen in Blasenstromungen berucksichtigt. Der Zerfall und die Koaleszenz der Blasen werden durch eine physikalisch begrundete Modellbildung beschrieben. Die Stromungsfelder werden fur zylindrische Blasensaulen ohne Einbauten mit Hilfe des Euler-Euler-Verfahrens berechnet. Hierbei werden die Klein- und Grosblasen als pseudo-kontinuierliche Phasen neben der flussigen Phase berucksichtigt. Die berechneten Stromungsfelder sind durch zahlreiche grosraumige Wirbel gekennzeichnet. In ihnen sind die Felder der Phasenanteile von Gas und Flussigkeit inhomogen und zeitlich sowie ortlich veranderlich. Die berechneten Phasenanteile, Geschwindigkeiten und Blasengrosen stimmen mit den Ergebnissen experimenteller Untersuchungen an Blasensaulen im Durchmesserbereich bis 0,3 m uberein. Coupled Calculation of Bubble Size Distribution and Flow Fields in Bubble Columns In this paper the use of computational fluid dynamics (CFD) for the calculation of flow fields in bubble columns is explained. The local bubble size distribution is considered with the aid of a simplified balance equation for the average bubble volume in bubbly flow. Models are developed for the rate of bubble break-up and coalescence based on physical principals. The flow fields in cylindrical bubble columns without internals are calculated using the Euler-Euler method. The small and large bubble fraction are considered as pseudo-continuous phases in addition to the liquid phase. The calculated flow fields are characterised by several large scale vortices. The local volume fractions of gas and liquid are very inhomogeneous and highly time dependent. The calculated volume fractions, velocities and bubble size distributions agree well with experimental results for bubble columns up to 0.3 m in diameter.

The importance of the rise angle of bubbles on the influence of local bubble-size distribution in fluidized beds was studied. A new method is proposed for transforming chord-length distribution to a local bubble-size distribution, including the effect of the velocity vector direction on the transformation. Monte-Carlo simulation was used to generate bubbles synthetically with several rise angles, based on the fact that the velocity vector direction distribution of bubbles was a Bingham distribution. The transformation of chord-length data obtained by an imaginary probe, using the Parzen window as an estimation of the probability density function, gives a good estimation of the local bubble-size distribution for different rise angles and the new approach offered in this paper, knowing that the direction of the velocity vector direction for any orientation of the bubbles in the fluidized bed gives a superior agreement than the approach where the local bubble-size distribution is estimated from bubbles with vertical rises.

A study was conducted to characterize bubble formation behavior of pressurized microporous hollow fiber membranes with water flow normal to the fiber axis. The influence of operating conditions such as water velocity (0.07 to 0.6 m/s), gas pressure (275 to 380 kPa), and gas fluxes (0.001 to 0.02 m/s) on bubble formation behavior was examined. Within these operating conditions, bubbles with a diameter smaller than a 100 μm were formed at the membrane surface. Coalescence occurred close to the membrane, which resulted in bubble diameters of 100 to 500 μm above the fiber. Bubble diameters increased with increasing gas flow rate and decreasing water velocity. These effects are expected as they both lead to increased local bubble density and rates of coalescence. Bubble formation behavior of the membrane was predicted well by an empirical equation determined for a single orifice by Ito and Hirata.

Bubble behavior, including bubble Sauter diameter, bubble rise velocity, bubble frequency and local gas holdup in different radial and axial positions, was measured using a dual electro-conductivity probe in air-water-glass beads fluidization systems. It has been found that the bubble characteristics differ significantly in various flow regimes, depending on the operating conditions; the radial distribution of bubble parameters also changes from one flow regime to another. Thus, it is necessary to employ local bubble behavior in the modeling of three-phase fluidized beds. Le comportement des bulles, et notamment le diametre des bulles de Sauter, la vitesse d'ascension des bulles et la retention de gaz locale dans des positions radiales et axiales differentes, a ete mesure a l'aide d'une sonde d'electro-conductivite duale dans des systemes de fluidisation a billes air-eau-verre. On a trouve que les caracteristiques des bulles variaient de facon significative dans divers regimes d'ecoulement selon les conditions de fonctionnement; la distribution radiale des parametres des bulles change avec le regime d'ecoulement. C'est pourquoi le comportement des bulles local est a inclure dans la modelisation des lits fluidises triphasiques.

Bubble-size distributions influence the behavior of multiphase systems, but are not readily measured directly using probes. The chord lengths may be transformed into bubble sizes by modeling the bubble shapes as ellipsoids. Previous research on the transformation of chord-length data into bubble-size distributions using a numerical backward transformation revealed an instability problem. This problem was overcome by transforming the chord-length data to a local bubble-size distribution directly by using a Parzen window function and summing to yield the whole distribution. The best estimate of the local bubble-size density distribution depends on the Parzen window width that was chosen by proposing a measure of performance. An empirical relationship was also offered to determine the best Parzen window width. Chord lengths were generated using the example of a Rayleigh bubble-size distribution and Monte-Carlo simulation. The window approach transformed the chord lengths back into the bubble-size distribution with good agreement.

Optical probes are used to study gas-solid fluidized-bed hydrodynamics. The probes each consisting of a light source and photodetector separated by a gap are suitable for use at combustion-level temperatures. The methodology to process the signal for calculation of bubble properties such as bubble frequency, local bubble residence time, bubble velocity, pierced length, bubble size, and visible bubble flow is presented. The signal processing technique is independent of bed operating conditions. The probe signal processing methodology is validated by comparing calculated bubble properties based on the probe signal with properties observed on videotapes of a 2-D bed.

Bubble properties in stirred tank bioreactors equipped with standard radial flow Rushton turbines have been investigated. Bubble velocity patterns within a stirred tank reactor were derived from measured local bubble velocity distributions. Local information on specific interfacial areas, bubble number densities and bubble diameters together with local gas hold-ups, measured in a model medium at gas flow rates which are employed in practice, is presented. All measurements were performed with two new ultrasound pulse techniques which can be used in model as well as during real cultivation processes.

New data and analyses are presented for describing gas and solids behavior in a slurry bubble column. Axial solids concentration and bubble size distributions were measured in a 0.108 m ID slurry bubble column apparatus operated at steady state conditions. The column was operated with and without internal baffles. The slurry and gas superficial velocities ranged from 0.0077 to 0.009 m/s and from 0.031 to 0.24 m/s, respectively. The solid phase consisted of glass spheres in a narrow size range with a mean diameter of 96.5 μm; the liquid phase consisted of tap water. With a one-dimensional sedimentation-dispersion model, the data have been used to predict average solids loadings and axial distributions of the solids for specified operating conditions. Local bubble size and concentration measurements indicate that the slurry bubble column was operated in the churn-turbulent flow regime throughout the entire range of operating conditions used in this study. The impact of internal baffles and solids concentration on the gas and solids behavior is discussed.

The local bubble frequency, the local phase holdups and the local bed porosity in three-phase fluidized beds were measured. Air, water, and 250 μm glass beads were used as the gas, liquid, and solid phases. The effects of gas and liquid velocities on phase holdups were studied. Time-averaged local gas holdup and bubble frequency were measured by an optical fiber probe. Mass balances were performed at various axial positions along the fluidized beds to check the accuracy of the measurements.

A photographic study was made to investigate the boiling phenomena in the neighborhood of the critical heat flux. The system consisted of an electrically heated zirconium ribbon, insulated on its underface, suspended in a pool of water at its saturation temperature. Measurements of bubble diameters, bubble positions relative to the heating surface, local bubble frequencies, and contact angles at known times intervals were obtained from the film. Results indicate that at high heat fluxes the primary forces acting on a bubble leaving the surface are the buoyancy and drag forces. A dimensionless relationship is developed relating bubble velocity, bubble diameter, and contact angle at breakoff. Drag coefficients for freely rising vapor bubbles a saturated liquid are found to be representable by the usual drag coefficient-Reynolds number curves for solid bodies. Jakob's plot of bubble frequency vs. bubble diameter at breakoff is extended to high heat-flux values, and a relationship proposed by Deissler at the critical heat flux is found to yield reasonable agreement with the experimental data.